package la.renzhen.rtpt.admin.util;

/**
 * <p>
 *
 * @author <a href="mailto:zhouhaichao@2008.sina.com">haiker</a>
 * @version 01/06/2018 5:04 PM
 */
public class Strings {

    public static String empty(String a, String b) {
        if (a == null || "".equals(a.trim())) {
            return b;
        }
        return a;
    }

    public static String empty(String a) {
        if (a == null) {
            return "";
        }
        return a.trim();
    }

    /**
     * 安全截取操作<p>
     *
     * @param str   需要截取的字符串
     * @param start 截取开始字段
     * @param end   截取结束字段
     * @return 截取的字符串
     */
    public static String sub(String str, int start, int end) {
        if (str == null || "".equals(str)) {
            return "";
        }
        int length = str.length();
        if (start > length - 1) {
            return "";
        }
        if (end == 0 || end > length) {
            end = length - 1;
        } else if (end < 0) {
            end = length + end;
        }

        if (start >= end) {
            return "";
        }

        return str.substring(start, end);
    }
}
